Chappell Roan caused a stir on the red carpet, putting a photog on blast ... then literally set the stage on fire with a passionate performance of her hit, "Good Luck Babe."

Eminem had millennials feeling nostalgic ... his performance of "Houdini" saw him surrounded by look-alikes, a throwback to the VMAs 24 years ago. He also performed his collab "Somebody Save Me" with Jelly Roll guest-appearing on the big screen.

On that theme, LL Cool J was joined by Public Enemy's Flavor Flav and Chuck D to perform their old-school hits "Mama Said Knock You Out" and "Bring the Noise."

Sabrina gave an out-of-this-world performance with a medley of chart-toppers "Please, Please, Please," "Taste" and "Espresso." Then she planted a kiss on a blue female Martian ... prompting a number of "transgender operations on illegal immigrants" jokes inspired by this week's presidential debate.

Katy Perry killed it, singing some of her biggest hits, including "Dark Horse," "E.T.," "Teenage Dream," "I Kissed a Girl," "Firework" and "Lifetimes." Orlando Bloom presented her with this year’s Video Vanguard Award -- planting a big kiss on her fiancé after her performance. And Doechii joined KP onstage for the live debut of their collaboration "I'm His, He's Mine."

Karol G also rocked the stage with her new single "Si Antes Te Hubiera Conocido," getting the audience into it -- Taylor Swift and Camila Cabello were on their feet dancing along with her.

Tay Tay went into the evening with the most nominations, taking home 7 awards  ... Her boyfriend Travis Kelce did not attend the show, but she did give him a big shout-out in her Video of the Year acceptance speech. And Flav gave a custom gift to co-presenter, Olympian Jordan Chiles.